1. Field of the Invention
The present invention relates to a device for guiding a hollow blank emerging from a cross-rolling mill and in particular, an Assel mill, wherein the hollow blank is rotated about a longitudinal axis.
2. Description of the Related Art
A hollow blank rolled in a cross-rolling mill, especially an Assel mill, emerges from the rolling mill at a certain speed while rotating about its own axis. The movement of the hollow blank during the delivery stage of the rolling process must be controlled or supported by suitable guides until, upon termination of the rolling process, the blank is transported to the next roller table. In the prior art, a number of fairly expensive proposals for the delivery guides have been made, some of which have been functionally implemented and demonstrated.
The known delivery guides are inadequate, however, especially in machines that roll hollow blanks with extremely large d/s ratios (for example, d/s=50), because at high temperatures thin-walled blanks transmit only very small bending and torsion moments. If during delivery a hot hollow blank impacts even small edges, or if its forward motion is otherwise hindered, e.g., by diameter fluctuations in the hollow blank, then vibrations or blockages quickly arise, and the hollow blank warps in a wave-like manner. This leads to vibrations, which can be so strong that the rolling process must be broken off.
Even in relatively smooth rolling processes, the friction force to be overcome increases along with the rolled length, and thus the mass, of the hollow blank. Under some circumstances, if the rotational movement of the hollow blank during delivery is not supported by suitable components, the friction force to be overcome by the dead weight can become so great that the transmittable torsion moment is exceeded and the hollow blank is twisted.
A further disadvantage of the known prior art is that unclean guides in the entry and delivery sections of a rolling mill negatively effect tolerances and thus impair quality.